Not Applicable
The present invention is in the field of devices used to subject portions of a blood vessel to nuclear radiation to prevent restenosis of the irradiated area after performance of an angioplasty procedure.
A common problem after performance of a percutaneous transluminal coronary angioplasty is the restenosis of the treated area. In fact, restenosis occurs in 30% to 50% of cases. Restenosis occurs, at least in part, as a result of vascular smooth muscle cell migration, proliferation, and neointima formation at the site of the angioplasty. It has been shown that intracoronary delivery of ionizing radiation causes focal medial fibrosis, which when delivered at the site of the angioplasty, impedes the restenosis process. Adjacent coronary segments and the surrounding myocardium are undamaged by the irradiation treatment.
Delivery of the ionizing radiation at the site of the stenosis can be achieved by the introduction of an irradiation source, such as a ribbon, through an infusion catheter. In known systems, the infusion catheter is inserted to the site of the stenosis over a guidewire which may be inserted before, or alternatively, left after, the performance of an angioplasty procedure. After insertion of the infusion catheter, the guidewire is removed from the catheter, and the irradiation ribbon is inserted in its place. The irradiation ribbon typically incorporates a plurality of Iridium-192 seeds or pellets near its distal end. Other sources that might not be line sources of ionizing radiation can be used, as well. This plurality of radioactive sources arranged essentially in a line approximates a line source, although the intensity of the radiation will vary axially to some extent, depending upon the spacing and length of the seeds. The irradiation ribbon is inserted to the point where the radioactive material is placed in the area of the stenosis. The Iridium-192 emits gamma radiation having a range of energies between 296 and 612 thousand electron volts (keV).
The currently known systems have several disadvantages. First, the guidewire must be withdrawn before insertion of the irradiation ribbon. Withdrawal of the guidewire is not favored by physicians because it adds at least one step to the procedure, and because it takes additional time. The performance of any additional step presents additional opportunities for complications. Time is of the essence during angioplasty because much of the procedure involves at least partial blockage of the flow of blood in the blood vessel, which can be harmful to the muscle served by the vessel. This problem is compounded during the irradiation procedure, since the radioactive source must often be left in place for several minutes in order to deliver the desired dose of radiation to the vascular tissue. The time problem can be further compounded by the need to reinsert the guidewire after delivering the radiation, in some cases. In solving the problem of guidewire placement, it must be kept in mind that the irradiation catheter is often used in very small blood vessels, so it can be desirable to keep the overall diameter of the catheter as small as possible.
A second disadvantage of known systems is that the irradiation ribbon is exposed to blood flow in the infusion catheter, and it is even possible that some of the radioactive seeds could be lost out the distal end of the infusion catheter, or the irradiation ribbon itself can break, releasing radioactive material into the blood. Even if the blood does not directly contact the radioactive material, if blood contacts the radiation source, or if the radiation source enters the sterile field on the operating table, the radiation source must be sterilized. This adds expense to the procedure, and it exposes sterilization personnel to ionizing radiation.
A third disadvantage of known systems is that location of the radioactive material radially within the blood vessel is largely uncontrolled. Rotation of the infusion catheter may assist in centering the radiation source within the stenosis, in some cases, but this method is not always effective. Centering of the radioactive material within the tissues injured by the angioplasty may be required, because it is important to deliver a known dose of radiation uniformly to the affected tissue. The intensity of gamma or beta radiation emanating from a [line] source varies inversely with the square of the radial distance from the source. Therefore, if the radiation source is not centered within the blood vessel, the dose delivered to one side of the vessel can vary greatly from the dose delivered to the opposite side. In addition, if the line source lies at an angle to the centerline of the vessel, rather than being concentric therewith, or at least parallel thereto, the dose delivered can vary axially by an appreciable amount, throughout the length of the stenosis. In some cases, it can even be desirable to position the radiation source parallel to, but offset from, the centerline of the blood vessel, if it is desired to irradiate one side of the stenosis more than the other side. This can be desirable if restenosis is expected to result more from proliferation of the tissues on one side than on the far side.
It is an object of the present invention to provide a catheter assembly for irradiation of a stenotic segment of a blood vessel, which can be inserted to the site of the stenosis over a guidewire. It is a further object of the present invention to provide a catheter assembly which can place an irradiation source at a desired location within a blood vessel, both axially and radially. It is a still further object of the present invention to provide a catheter assembly which allows the safe use of an unsterilized radiation source. It is a yet further object of the present invention to provide an irradiation catheter assembly which has a minimum overall diameter. Finally, it is an object of the present invention to provide a catheter assembly which is economical to manufacture and easy to use.
A summary of the preferred embodiment of the present invention follows for exemplary purposes. The present invention provides a catheter for use with an irradiation source, such as a ribbon, with the catheter being constructed to be inserted over a guidewire which is in place in the blood vessel. The catheter body has a radiation lumen into which the irradiation ribbon, or other radiation source, is inserted. The radiation lumen is sealed at the distal end of the catheter body to fully retain the irradiation ribbon and its incorporated radioactive material.
A guidewire channel is formed on the catheter body, separate from the radiation lumen, with at least a portion of the guidewire channel being formed near the distal end of the catheter body. In a first embodiment, the guidewire channel can be formed as a channel alongside the distal portion of the catheter body. In this first embodiment, the guidewire channel can be sufficiently long to reach the area of the stenosis while also passing through a guide catheter O-ring. A guidewire channel of this length provides a structure surrounding the guidewire, to allow sealing by a guide catheter O-ring. This first embodiment allows the irradiation catheter to be used through a guide catheter, providing a proximal fluid tight sealing surface against which the guide catheter O-ring can seal to allow injection of dye to aid in visualization of the radiation source, while simultaneously allowing free guidewire movement which can help position the irradiation catheter, as will be discussed below. Still further, this first embodiment of the guidewire channel can be formed with a lengthwise rupturable membrane. This essentially provides a distal portion of the guidewire channel for rapid exchange purposes, and a proximal portion of the guidewire channel for sealing purposes. In a second embodiment, the guidewire channel can be formed as only a short segment at the distal end of the irradiation catheter, beyond the distal end of the radiation lumen, allowing the use of the irradiation catheter as a rapid exchange catheter, as described in the patent applications cited earlier, upon which this application relies for priority. This second embodiment minimizes the overall diameter of the catheter, because the guidewire channel is not alongside the radiation lumen at any location. In both the first and second embodiments, the radiation lumen extends in a proximal direction beyond the proximal end of the guidewire channel. This proximal extension of the radiation lumen has a length sufficient to allow the proximal end of the radiation lumen to be handed outside the sterile field, into a non-sterile field, for insertion of the radiation source, while the proximal end of the guidewire channel remains within the sterile field. This allows use of a non-sterile radiation source, avoiding the necessity for sterilization, thereby saving sterilization costs, and eliminating radiation exposure of sterilization personnel.
Since it may be desirable to position the radiation source radially within the blood vessel, at least two methods, as well as several types of apparatus, are provided for accomplishing the radial positioning. A first method can be employed without any special apparatus, by introducing one or more bends in the guidewire, near its distal end. When the catheter and the irradiation ribbon are axially in place in the area of the stenosis, if the distal end of the catheter is not radially positioned as desired, the guidewire can be rotated to orient the bent portion of the guidewire in the direction in which it is desired to displace the catheter. Then, the guidewire can be slightly withdrawn, pulling one or more bends back into the distal end of the guidewire channel. The bend in the guidewire can cause the guidewire to exert a force against the wall of the guidewire channel, resulting in the desired flexing of the catheter body in the direction of the force, placing the distal end of the catheter in the desired radial location.
To implement an alternative method of use, the catheter may also be provided with a means for positioning the radiation source radially within the blood vessel. Most often, this positioning means will be used to center the radiation source radially. The irradiation catheter of the present invention can be used either with or without the positioning means. The positioning means can have various configurations, two examples of which are inflatable balloons and expandable wire loops. An inflatable balloon can be formed as a coil, or as a plurality of essentially annular balloons, or as a plurality of longitudinal lobes. The balloon or balloons can be connected to an inflation lumen formed on the catheter body, for inflation purposes.
Alternatively, a plurality of flexible wire loops can be mounted near the distal end of the catheter body, with one end of each loop fixedly attached to the catheter body, and one end free. The wire loops can be shaped to be self expanding when released, or the free end of each loop can be attached to an expansion means which is movable longitudinally by the user to move the free ends of the wire loops toward the attached ends. This movement causes the loops to expand outwardly. The loops can be mounted at spaced intervals about the periphery of the catheter body, to center the catheter within the blood vessel upon expansion. The expansion means can be relatively stiff wires designed to push on proximally located free ends of the wire loops, or they can be wires designed to pull on distally located free ends of the wire loops. Self expanding wire loops would expand without the aid of such expansion means, upon withdrawal of a retaining sheath.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: